The proposed research is designed to extend previous observations indicating that immune processes are subject to behavioral conditioning. Using an illness-induced taste aversion paradigm, rats and/or mice are conditioned by pairing a distinctively flavored drinking solution (the conditioned stimulus) with immunopharmacologic agents that may suppress or enhance immunologic reactivity (the unconditioned stimulus). After conditioning, all animals are treated with antigen (e.g., sheep erythrocytes). Antibody titers or cellular immune responses (delayed type hypersensitivity reactions) are measured after immunogenic stimulation in conditioned animals that are reexposed to the conditioned stimulus, conditioned animals that are not reexposed to the conditioned stimulus, conditioned animals injected with the immunopharmacologic agent, and in nonconditioned and placebo-treated groups. Current studies are directed to defining those parameters of the conditioning process and those parameters of antigenic stimulation and the immune response that may be optimal for the conditioning of immunopharmacologic effects and to an examination of the immune processes that can be modulated by conditioning.